基于剪切试验的预应力锚杆变形性能分析

为了研究锚杆对节理剪切性能的作用机制和模式,开展了锚固节理岩体的实验室剪切试验,模拟了不同强度的岩体在剪力作用下的变形和受力特征,对比了锚杆加固前、后岩体的剪切变形规律,分析了节理岩体强度、预应力及锚固方式对节理的抗剪能力的影响,试验过程中通过应变片测点监测锚杆轴力的变化规律,研究了节理剪切过程中锚杆的轴向受力机制和变形特性。剪切试验完成后,取出剪切变形后的锚杆,统计了变形段长度与各参数之间的关系。通过试验结果分析,剪力-位移曲线存在明显的3个阶段:弹性阶段、屈服阶段和塑性强化阶段,曲线近似呈现双直线特征,弹性段锚杆主要发挥销钉作用;屈服段锚杆的轴向作用开始调动,锚杆同时存在销钉和约束作用;塑性段锚杆不再发挥销钉作用,只是依靠其轴向约束作用限制岩体的变形;曲线表现出韧性增强的剪切性能,这就使得锚杆锚固节理岩体的破坏特性由脆性转变为塑性,从而提高了岩体的稳定性和安全度。节理面的滑动对锚杆产生剪切作用,由于切向变形而产生了附加的锚杆轴向变形,锚杆的轴向应力随着剪切位移的增大呈增长的趋势,变形剧烈区域集中于节理面附近,且距离节理面越近其轴向应力增大越多。

Analysis of deformation characteristics of prestressed anchor bolt based on shear test

The shear tests of bolted jointed rock mass were carried out in the laboratory to study the mechanical behaviors of anchor bolt in the jointed rock mass. In the experiment, rock mass of different strength, anchorage mode and prestress were simulated, meanwhile, the deformation characteristics of anchor bolts were monitored to compare the shear deformation regularity before and after bolting and to analyse the influences of prestress, rock strength, anchorage mode on shear capacity of jointed rock mass. Change of axial force was monitored through the strain gauge to study the axial deformation mechanism and force characteristics of anchor bolts. The distorted anchor bolts were taken out to analyse the relationship between the deformation length and other parameters after shearing test. Several conclusions were derived from the results of above tests: Shear stress vs. displacement curves can be divided into three stages: elastic stage, yield stage and plastic hardening stage, and show a feature of approximate double-linear lines. In elastic stage, the bolts act as “pin”. In yield stage, the axial effect was activated and bolts functioned as both pin and confinement effect. In plastic stage, the bolts did not take the effect of pin, and just restricted the deformation of rock though its axial confinement effect. Shear load vs. displacement curves presented as plastic hardening mode, which means that the toughness of bolted jointed rock mass will be enhanced; and the failure mode changes from fracture mode into yield mode. So that the stability and safety of bolted jointed rock mass were improved. The bolt was sheared as a result of slippage of the joint and was led to additional axial deformation due to lateral deformation, the axial stress increased with the shear displacement. The region of distortion of the bolt concentrated nearby the joint surface and the closer to the joint surface, the more the augment of the axial stress was.